Effect of crowding on alate production of the Russian wheat aphid,Diuraphis noxia(Mordvilko) was tested using a low-density treatment of 10–20 aphids per plant and a high-density treatment of 150–200 aphids per plant. Student'stdistribution (P<0.01) indicates no significant difference between the low and high density treatments. A pressure chamber was used to quantify the amount of water stress in wheat. Wing pad formation began within the range of −0.51 and −0.61 MPa and ended within the range of −1.21 and −1.31 MPa. From this range in water potential values, six water potential treatment ranges were established. Our results show by curvilinear regression that a positive correlation exists (P<0.01) between alate production and the leaf water potential of wheat, with maximum alate production occurring between −0.79 and −1.03 MPa. These data suggest that a response of the host plant, which in part results from feeding damage, is causing the production of alates.